12,062 research outputs found
What brakes the Crab pulsar?
Optical observations provide convincing evidence that the optical phase of
the Crab pulsar follows the radio one closely. Since optical data do not depend
on dispersion measure variations, they provide a robust and independent
confirmation of the radio timing solution. The aim of this paper is to find a
global mathematical description of Crab pulsar's phase as a function of time
for the complete set of published Jodrell Bank radio ephemerides (JBE) in the
period 1988-2014. We apply the mathematical techniques developed for analyzing
optical observations to the analysis of JBE. We break the whole period into a
series of episodes and express the phase of the pulsar in each episode as the
sum of two analytical functions. The first function is the best-fitting local
braking index law, and the second function represents small residuals from this
law with an amplitude of only a few turns, which rapidly relaxes to the local
braking index law. From our analysis, we demonstrate that the power law index
undergoes "instantaneous" changes at the time of observed jumps in rotational
frequency (glitches). We find that the phase evolution of the Crab pulsar is
dominated by a series of constant braking law episodes, with the braking index
changing abruptly after each episode in the range of values between 2.1 and
2.6. Deviations from such a regular phase description behave as oscillations
triggered by glitches and amount to fewer than 40 turns during the above
period, in which the pulsar has made more than 2.0e10 turns. Our analysis does
not favor the explanation that glitches are connected to phenomena occurring in
the interior of the pulsar. On the contrary, timing irregularities and changes
in slow down rate seem to point to electromagnetic interaction of the pulsar
with the surrounding environment.Comment: 11 pages, 8 figures, 3 tables; accepted for publication in Astronomy
& Astrophysic
Optical phase coherent timing of the Crab nebula pulsar with Iqueye at the ESO New Technology Telescope
The Crab nebula pulsar was observed in 2009 January and December with a novel
very fast optical photon counter, Iqueye, mounted at the ESO 3.5 m New
Technology Telescope. Thanks to the exquisite quality of the Iqueye data, we
computed accurate phase coherent timing solutions for the two observing runs
and over the entire year 2009. Our statistical uncertainty on the determination
of the phase of the main pulse and the rotational period of the pulsar for
short (a few days) time intervals are s and ~0.5 ps,
respectively. Comparison with the Jodrell Bank radio ephemerides shows that the
optical pulse leads the radio one by ~240 s in January and ~160 s in
December, in agreement with a number of other measurements performed after
1996. A third-order polynomial fit adequately describes the spin-down for the
2009 January plus December optical observations. The phase noise is consistent
with being Gaussian distributed with a dispersion of s in most observations, in agreement with theoretical expectations for
photon noise-induced phase variability.Comment: 10 pages, 5 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Managing knowledge in organizations : a Nonaka’s SECI model operationalization
Purpose: The SECI model (Nonaka, 1994) is the best-known conceptual framework for understanding knowledge generation processes in organizations. To date, however, empirical support for this framework has been overlooked. The present study aims to provide an evidence-based groundwork for the SECI model by testing a multidimensional questionnaire Knowledge Management SECI Processes Questionnaire (KMSP-Q) designed to capture the knowledge conversion modes theorized by Nonaka.
Methodology: In a twofold study, the SECI model was operationalized via the KMSP-Q. Specifically, Study One tested its eight-dimensional structure through exploratory and confirmatory factorial analyses on 372 employees from different sectors. Study Two examined the construct validity and reliability by replicating the KMSP-Q factor structure in knowledge-intensive contexts (on a sample of 466 health-workers), and by investigating the unique impact of each dimension on some organizational outcomes (i.e., performance, innovativeness, collective efficacy).
Findings: The overall findings highlighted that the KMSP-Q is a psychometrically robust questionnaire in terms of both dimensionality and construct validity, the different knowledge generation dimensions being specifically linked to different organizational outcomes.
Research/Practical Implications: The KMSP-Q actualizes and provides empirical consistency to the theory underlying the SECI model. Moreover, it allows for the monitoring of an organization’s capability to manage new knowledge and detect the strengths/weaknesses of KM-related policies and programs.
Originality/Value: This paper proposes a comprehensive measure of knowledge generation in work contexts, highlighting processes that organizations are likely to promote in order to improve their performance through the management of their knowledge resources
Aqueye+: a new ultrafast single photon counter for optical high time resolution astrophysics
Aqueye+ is a new ultrafast optical single photon counter, based on single
photon avalanche photodiodes (SPAD) and a 4-fold split-pupil concept. It is a
completely revisited version of its predecessor, Aqueye, successfully mounted
at the 182 cm Copernicus telescope in Asiago. Here we will present the new
technological features implemented on Aqueye+, namely a state of the art timing
system, a dedicated and optimized optical train, a high sensitivity and high
frame rate field camera and remote control, which will give Aqueye plus much
superior performances with respect to its predecessor, unparalleled by any
other existing fast photometer. The instrument will host also an optical
vorticity module to achieve high performance astronomical coronography and a
real time acquisition of atmospheric seeing unit. The present paper describes
the instrument and its first performances.Comment: Proceedings of the SPIE, Volume 9504, id. 95040C 14 pp. (2015
Neutrino Mass Squared Differences in the Exact Solution of a 3-3-1 Gauge Model without Exotic Electric Charges
The mass splittings for the Majorana neutrinos in the exact solution of a
particular 3-3-1 gauge model are computed here in detail. Since both
and the mass splittings ratio
are taken into account, the analytical calculations
seem to predict an inverted mass hierarchy and a mixing matrix with a texture
based on a very close approximation to the bi-maximal mixing. The resulting
formulas for the mass squared differences can naturally accomodate the
available data if the unique free parameter () gets very small values
(). Consequently, the smallness of the parameter requires
(according to our method) a large breaking scale TeV
in the model. Hence, the results concerning the neutrino mass splittings may
lead to a more precise tuning in the exact solution of the 3-3-1 model of
interest, being able - at the same time - to recover all the Standard Model
phenomenology and predict the mass spectrum of the new gauge bosons
in accordance with the actual data. The minimal absolute mass
in the neutrino sector is also obtained - eV - in the case
of our suitable approximation for the bi-maxcimal mixing.Comment: 10 pages, no figure
Pre-MS depletion, accretion and primordial 7Li
We reconsider the role of pre-main sequence (pre-MS) Li depletion on the
basis of new observational and theoretical evidence: i) new observations of
Halpha emissions in young clusters show that mass accretion could be continuing
till the first stages of the MS, ii) theoretical implications from
helioseismology suggest large overshooting values below the bottom of the
convective envelopes. We argue here that a significant pre-MS 7Li destruction,
caused by efficient overshoot mixing, could be followed by a matter accretion
after 7Li depletion has ceased on MS thus restoring Li almost to the pristine
value. As a test case we show that a halo dwarf of 0.85 Msun with an extended
overshooting envelope starting with an initial abundance of A(Li) = 2.74 would
burn Li completely, but an accretion rate of the type 1e-8xe^{-t/3e6} Msun
yr would restore Li to end with an A(Li) = 2.31. A self-regulating
process is required to produce similar final values in a range of different
stellar masses to explain the PopII Spite plateau. However, this framework
could explain why open cluster stars have lower Li abundances than the
pre-solar nebula, the absence of Li in the most metal poor dwarfs and a number
of other features which lack of a satisfactory explanation.Comment: To be published in Memorie della Societ\`a Astronomica Italiana
Supplementi Vol. 22, Proceedings of Lithium in the cosmos, Iocco F.,
Bonifacio P., Vangioni E., ed
Effects of frequency correlation in linear optical entangling gate operated with independent photons
Bose-Einstein coalescence of independent photons at the surface of a beam
splitter is the physical process that allows linear optical quantum gates to be
built. When distinct parametric down-conversion events are used as an
independent photon source, distinguishability arises form the energy
correlation of each photon with its twin. We find that increasing the pump
bandwidth may help in improving the visibility of non-classical interference
and reaching a level of near perfect indistinguishability. PACS: 03.67.Mn,
42.65.Lm, 42.50.St.Comment: Replaced with published versio
Logarithmic SUSY electroweak effects on four-fermion processes at TeV energies
We compute the MSSM one-loop contributions to the asymptotic energy behaviour
of fermion-antifermion pair production at future lepton-antilepton colliders.
Besides the conventional logarithms of Renormalization Group origin, extra SUSY
linear logarithmic terms appear of "Sudakov-type". In the TeV range their
overall effect on a variety of observables can be quite relevant and
drastically different from that obtained in the SM case.Comment: 19 pages and 14 figures, corrected version. e-mail:
[email protected]
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